Abstract
Increased anthropogenic CO2 emissions are leading to an increase in CO2 uptake by the world's oceans and seas, resulting in ocean acidification with a decrease in global ocean water pH by as much as 0.3–0.4 units by the year 2100. The direct effects of changing pCO2 on important microalgal feedstocks are not as well understood. Few studies have focused on lipid composition changes in specific algal species in response to ocean acidification and yet microalgae are an indispensable food source for various marine species, including juvenile shellfish. Isochrysis galbana and Tetraselmis suecica are widely used in aquaculture as feeds for mussels and other shellfish. The total lipid contents and concentrations of I. galbana and T. suecica were investigated when grown under present day (400 ppm) and ocean acidification conditions (1000 ppm) to elucidate the impact of increasing pCO2 on an important algae feedstock. Total lipids, long-chain alkenones (LCAs) and alkenoates decreased at 1000 ppm in I. galbana. I. galbana produces higher lipids than T. suecica, and is perhaps as a result more impacted by the change in carbon available for lipid production under higher pCO2.I. galbana is an important feedstock, more easily assimilated for growth in juvenile shellfish and reductions in lipid composition may prove problematic for the growth of future shellfish aquaculture. Our findings suggest that higher pCO2 impacts on algal lipid growth are species specific and warrant further study. It is therefore vital to examine the impact of high CO2 on algal lipid production, especially those commercial shellfish feed varieties to predict future impacts on commercial aquaculture.
Highlights
Increased anthropogenic CO2 emissions are leading to an increase in CO2 uptake by the world's oceans and seas, resulting in a decrease in global ocean water pH by as much as 0.3–0.4 units by the year 2100 (IPCC, 2013)
The lipid profiles for each species of algae were not affected by the change of pressure CO2 (pCO2) level, which means that the same lipids were observed at 400 ppm pCO2 and 1000 ppm pCO2 for I. galbana and T. suecica
The fact that concentrations of the total lipids, fatty acids, sterols, long-chain alkenones (LCAs) and alkenoates decreased at 1000 ppm in I. galbana contradicts biofuel studies examining lipid composition under experimental rapid growth in higher CO2 (Nakanishi et al, 2014; Singh & Singh, 2014; Tanadul, Vandergheynst, Beckles, Powell, & Labavitch, 2014)
Summary
Increased anthropogenic CO2 emissions are leading to an increase in CO2 uptake by the world's oceans and seas, resulting in a decrease in global ocean water pH by as much as 0.3–0.4 units by the year 2100 (IPCC, 2013). Further work by Fitzer et al (2015) found that both the newest and older calcite of Mytilus edulis grown under high pCO2 (1000 ppm) for a period of 6 months were harder and more brittle and fractured more . These shells would be more susceptible to breakage from industry or predation (Fitzer et al, 2015). When mussels were reared in an environment with a high concentration of nutrients in the water column, inner shell corrosion was only visible in the specimens
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